1. Field of the Invention
The present invention concerns a method of and an apparatus for decomposing wastes in a chemical plant of decomposing wastes containing by-products formed in a chemical plant by using super-critical or high pressure/high temperature water and capable of recovering and reutilizing raw material compounds or derivatives thereof as an aimed product in a plant from the wastes. More in particular, it relates to a method of and an apparatus for decomposing wastes such as PET bottles and urethane foams by using super-critical water and high pressure/high temperature water and recovering the raw material compounds or the derivatives thereof from the wastes.
2. Description of the Prior Art
In the case of industrially synthesizing various chemical products in chemical plants, it is well-known that by-products other than aimed products are formed or unreaction products remain. For example, in a polymerizing reaction plant, a device for separating a resultant polymer and unreacted monomers in a reaction vessel is essentially provided and the recovered unreacted monomers are generally reutilized as the raw material for the polymerizing reaction. It is also known that oligomers are by-produced in the polymerizing reaction and separation/elimination steps of the oligomers are often conducted since aimed properties can not be obtained or the properties are worsened with lapse of time if the oligomers are left in the polymers. While the unreacted monomers can be reutilized by merely incorporating them again into a raw material feed line, the oligomers are subjected to incineration or discarding since they can not be handled in the same manner as the monomers.
Side reaction products or oligomer such as dimers or trimers of aimed compounds are formed not only in polymerizing reaction plants but also in chemical plants for synthesizing low molecular compounds, and such by-products or oligomers have to be separated from the aimed compounds by, for example, distillation. While by-products can be separated from low molecular materials relatively easily, since separation of the aimed compound from the oligomers is often difficult, a great amount of the oligomers and the aimed compounds are often contained after all in the wastes such as distillation residues. There are scarcely no methods of effectively utilizing such wastes and they are merely subjected to incineration or discarding treatment, which brings about a problem with a view point of resource saving.
In recent years, it has been attempted to detoxicating wastes or obtain utilizable products therefrom by using hydrolyzing or oxidizing reactions in super-critical water or high pressure/high temperature water. For example, Japanese Patent Laid-Open Hei 3-500264 discloses a method of detoxicating wastes in a discharge liquid system by utilizing oxidizing reaction under a super (or sub)-critical state, Japanese Patent Laid-Open Hei 5-31000 discloses a method of hydrolyzing various high molecular compounds by using water at a super-critical or subcritical state and, further, Japanese Patent Publication Hei 3-16328 or Japanese Patent Laid-Open Hei 5-271328 discloses a method of obtaining pure terephthalic acid and glycol from polyethylene terephthalate wastes.
However, although the technique of Japanese Patent Laid-Open Hei 3-500264 is important as a detoxicating method, it involves a problem for the usefulness of the resultant materials since the method accompanies oxidizing reaction and other publications mention nothing about methods and apparatus of efficiently decomposing wastes in chemical plants containing oligomers such as dimers.